What roof will protect against a lightning strike?

Even a person who little understands in physics will say that first of all, it is necessary to protect the roof of the building. Indeed, a lightning strike is primarily directed to the roof. But, the roofing, the objects and designs that are placed on it, suffer. Lightning rods are created to take the electric charge from the building tops.

Metal roofings

But is not it easier to create a roofing that can withstand a lightning strike? It turns out, that such coatings exist. The steel sheet with the thickness of more than 4 mm will perfectly transfer any strike. A copper plate with such a resistance must have a thickness more than 5 mm, aluminum - more than 7 mm. However, such a coating will be too heavy, which can only be withstanded by a palace or a castle.

Metal tile roofing and profiled metal

Usual cottages and townhouses are satisfied with metal tile roofing or profiled metal, the thickness of which does not exceed 1 mm. The standard IS-153-34.21.122-2003 allows the lack of protection of such a roof, but it must:

be grounded;
not have any structure under it (trussing, sheathing), supporting combustion.

It doesn't fit Russian houses, since domestic construction techniques almost always provide the use of wood for such constructions, as it burns excellently. Therefore, lightning protection of residential and public buildings in Russia is necessary.

Dielectric roofing

Asbestos slate becomes the thing of the past. Its negative impact on the environment has been proved. This material is now almost not used to cover residential, commercial and industrial buildings, that is why, we will considere synthetic coating in the category of dielectric roofing. At a lightning strike into the roof covered with synthetic material, a powerful electrical charge will go through it in a fraction of a second.

Even an average lightning has the intensity of more than a million volts, it will freely pass through this unserious barrier and having flown around the building will stop at some ungrounded element. It may be a pipe or an interior electrical network wire. The potential of the network 380/220 V is considered to be zero for lightning! You can guess the consequences of its strike into the wiring of the house.

Reinforced concrete slabs

Even a direct lightning strike can destroy the roof covered with reinforced concrete slabs. They are quite strong. When lightning strikes them, there appears a small hole, which won't entail destruction of the slab. However, there is a range of other dangers. The current from the lightning spreads along the reinforcement inside the concrete base. According to the standards, laying of reinforced concrete slabs is accompanied by the assembly of layers of hydro and thermal insulation, the materials of which are flammable or fusable.

As prescribed, in order to arrange lightning protection of residential and public buildings with concrete roofs, a metal mesh must be put on top. Its purpose is to take the electrical load during a lightning strike upon itself. However, no expert can explain to you, how a metal mesh with the cells of 12 x 12 m, elevating from the concrete level to a few millimeters, will protect against a direct lightning strike.

According to the standard IS-153-34.21.122-2003 the distance from the roof to the lightning rod must be at least 15% of the height of the building, that is a few meters. Despite this, the metal grid without fail is placed on top of concrete slabs, supposedly to protect against lightning.But bitumen, which mostly coveres concrete roofs, perfectly suits the role of the security cover. It can counteract a lightning strike, although the nature of this property has not been studied. Nobody studied it seriously.

The material was created on the basis of an article by Professor Eduard Meierovich Bazelyan "Consider the frequency of lightning strikes into the building".

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